So, when you run the hull on a motor, you will have a fountain up the daggerboard trunk. You will need to seal it off. What I did was make a plug that fills the trunk. I laminated AZEK trim as it is soft and I hope will crush under ice, and not damage the trunk. I built a large flange on the top of the plug and then made a neoprene gasket (old waders) and using 6 or 8 screws sealed it at the deck. It does not leak, and can be removed to sail. I did my build back in 2009 so you can search and see build pictures.